1. Field of the Invention
The proposed invention relates to a method for forming a gate with metal silicide and more particularly to a method that effectively eliminates gate edge leakage of the metal silicide gate.
2. Description of the Prior Art
In contemporary semiconductor technology, a gate usually is formed by the following process: as FIG. 1A shows, the formation of a dielectric layer 11 and conductor layer 12 on substrate 13 in sequence; as FIG. 1B shows, patterning the position of a gate by photoresist 14; and then as FIG. 1C shows, etching these layers to form the required gate and then the removal of photoresist 14.
Moreover, because some scars 15 are formed on the sidewall of the dielectric layer during the etching process, the quality of dielectric layer 11 is degraded and it is called a xe2x80x9cgate edge defect.xe2x80x9d A popular method for dealing with this issue is to eliminate these scars 15 by performing an oxidation process after the etching process and before a spacer is formed. Obviously, the efficiency of the oxidation process is more enhanced when the dielectric layer 11 is an oxide layer.
However, when metal silicide is used to reduce resistivity and is formed as a part of gate, a new issue arises because the oxidation process not only repairs scars but also oxidates the metal silicide layers, and then resistivity of the metal silicide layer is increased. In other words, improvement of the dielectric layer accompanies degradation of the metal silicide layers, and then the degraded quality of the gate is unavoidable. In addition, because TiSi2 is liable to be oxidated more than other popular metals silicide such as CoSi2, WSi2, PtSi2, MoSi2, PtSi2 or TaSi2, the issue is more serious when the metal silicide layer is a TiSi2 layer.
In summary, it is desired to develop a new method that repairs scars without defalcation with the metal silicide layer being oxidated. Particularly, the new method is more important when the metal silicide layer is indispensable.
A principal object of the present invention is to provide a manufacturable method for forming a gate with a metal silicide.
Another object of the present invention is to provide a practical method that eliminates the edge defect without increased resistivity of a metal silicide.
A present preferred embodiment of the invention is a method for forming a gate with a metal silicide. In short, the proposed method comprises the following steps: providing a substrate; forming a first dielectric layer on the substrate; forming a polysilicon layer on the first dielectric layer; forming a metal silicide layer on the polysilicon layer; forming a second dielectric layer on the metal silicide layer; etching these layers to form a gate on the substrate; performing a thermal nitridation process to form a metal nitride layer on sidewall of the metal silicide layer; and performing a thermal oxidation process to eliminate the edge defect.
Another preferred embodiment is a re-oxidation process for a Ti-polycide gate. First, a substrate is provided; then, an oxide layer is formed, followed by the formation of polysilicon layer, a Ti-polycide layer and a silicon nitride layer on the substrate in sequence; and then etching a silicon nitride layer, a Ti-polycide layer, a polysilicon layer and an oxide layer to form a gate; next, a thermal nitridation process is performed to treat the gate; finally, a thermal oxidation process is performed to treat the gate.
In short, the nitridation process is the main characteristic of the invention. Herein, a metal nitride layer is formed on the sidewall of the metal silicide layer and then the remainder of the metal silicide layer is not affected by the following oxidation process.